1. Field of the Invention
The present invention relates to an image analysis apparatus, an image analysis program storage medium and an image analysis method for classifying an image included in a medical image on display, and an image processing apparatus, an image processing program storage medium and an image processing method for extracting the image of a subject included in the medical image on display.
2. Description of the Related Art
In the conventional medical field, a medical image photographed inside a subject using the X-ray photographic apparatus, the ultrasonic apparatus and the endoscopic apparatus are widely utilized for diagnosing the conditions of the subject, etc. By utilizing the medical image for diagnosis, the progress of the disease of the subject can be grasped without any external damage to the subject, and therefore, the information required for determining the treatment method can be easily obtained.
In addition to the X-ray photographic apparatus and the endoscopic apparatus, more and more hospitals have come to introduce the CT (Computerized Tomography) apparatus and the MRI (Magnetic Resonance Imaging) apparatus for photographing plural sectional images at each of the plural slice positions of the subject. The CT apparatus and the MRI apparatus, as compared with the endoscopic apparatus with an optical probe inserted in the body of the subject, can reduce the pain of the subject during the inspection, while at the same time three-dimensionally confirming the accurate position and size of the seat of a disease or the affected part using plural sectional images. In recent years, therefore, the CT and MRI apparatuses have come to be employed also for the purpose of the thorough physical examination.
In the CT and MRI apparatuses, the photographing operation is performed while the subject is laid on the diagnostic table, and therefore, the medical image photographed generally include also the diagnostic table, the cloth worn by the subject and the medical equipment located near the subject. Presently, the anomalous part considered the seat of a disease is automatically extracted by analyzing each pixel of the medical image or the degree of obesity is confirmed from the sectional area of the sectional image. In order to realize these processes, only the subject area associated with the subject in the medical image is required to be extracted with high accuracy.
In a widely-known method of extracting the subject area in the medical image, a high-density area having an image density not lower than a reference density is extracted as a subject area from the medical image taking advantage of the fact that the subject area associated with the subject has a higher image density than the remaining areas. According to this method, however, the area of the diagnostic table, etc. having an image density as high as the subject area is also extracted, and therefore, the user is required to take the trouble of manually removing the unrequited areas other than the subject area, thereby posing the problem a considerable time is required.
With regard to this problem, Japanese Patent Application Laid-Open (JP-A) No. 9-187444 discloses a method in which high-density areas having an image density not lower than a reference density are extracted and after executing the smoothing process using a median filter, the subject area is extracted based on the size of each high-density area. In the medical image after the smoothing process, however, the subject area undergoes only a small change while the contour line of the unrequited area such as the diagnostic table is discontinued, resulting in a reduced size of the unrequited area. In the method described in JP-A No. 9-187444, the unrequited area in the medical image is accurately removed by taking advantage of this feature, and therefore, the user is not required to take the trouble of manually removing the unrequited area, thereby facilitating the extraction of the subject area in the medical image.
While the unrequired area in the medical image is extracted with high accuracy, the use of the method described in JP-A No. 9-187444, however, leads to an erroneous recognition that the image area including the parts such as the throat, the ears and the nose connected to the body surface is erroneously extruded from the subject area. Also, the lung contains the air and therefore the image density of the lung area in the medical image is reduced, with the result that the lung area cannot be extracted as the subject area by the method described in JP-A No. 9-187444. After all, therefore, the technique described in JP-A No. 9-187444 poses the problem that the user is required to manually extract again the lung field, etc.
Another problem of the method described in JP-A No. 9-187444 is that one of the two legs of the subject is lost in the medical image, i.e. a small part imaged at a distance from the body fails to be included.